Improvement in the method of straightening the faces of millstones



. W..LEHMANN. t Method of Straightening the Faces of Millstones.

No.-2fl. 244. Pa tented Jan. 7, 1879.

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as to paint the elevated spots.

UNITED STATES PATENT 'FFICE.

,WILLIAM LEHMANN, OF MILWAUKEE, WISOON SIN.

IMPROVEMENT IN THE METHOD OF STRAIGHTENING THE FACES 0F MILLSTONES.

Specification forming part of Letters Patent No. 211,244, dated January7, 1879; application filed April 30,1878.

proved Method of Truing the Grinding-Surfaces of Millstones, of whichthe following is a specification:

My invention relates to an improved method of truing or testing theaccuracy of the grinding-surfaces of millstones; and consists inemployin g a straight staff having asmall painted I portion at thecenter, and passing this staff over the stone in such manner as to carrythe painted portion over every portion of the grinding-surface.

In order to secure a uniform and economical' grinding action on the partof millstones, it is necessary that that portion of their faces whichperforms the grinding operation shall be absolutely straight and true,and it is to secure this result, when the stones are being dressed, thatmy invention is designed.

Heretofore the universal practice in train g millstones has been to makeuse of two straight staffs, known as the proof-staff and thered-staiffithe latter being so designated be cause its entire undersurface was coated with a colored chalk or paint to be transferred tothe face of the stone.

In commencing operationon a stone under the common method, theproof-staff is applied to the face of the stone, and such places asappear to be above the general level are marked and colored or painted.These spots are then cut down by hand, the high spots again marked andcut down, and so on repeatedly until no high places are appreciable tothe touch. The red-staff is then painted on on its whole under surface,laid across the stone, generally at one side of the bosom, and thenswung around over the entire surface, so The high spots are thenreduced, the test repeated, and the operation continued until the staffpaints the entire surface, whereupon the stone is considered to be astrue as possible.

In practice it is found that a true level surface cannot be producedinthe abovedescribed manner, and that the staff painted its entire lengthwill not indicate a true surface-first, because it will rock or pivotupon the high points so that its ends will fall into the low I pointsand paint them as well as the high; and, second, because the sections ofwhich grinding-stones are composed vary in hardness, so that the staffhaving its entire surface pain ted will mark one spot more heavily thananother, although they may be on the same level.

After many experiments I have discovered that the above-mentioneddifficulties may both be overcome, and a true. surface secured by simplyproviding the red-staff with paint or color at the middle for a shortdistance, varyin g from one-half an inch to six or seven inches,according to the length of the staff, and then passing the staff overthe stone in such manner that the painted portion shall pass over everypoint in the grinding-surfaces, care being taken in so doing to keep asgreat a portion of the staffs length upon the stone as possible, inorder that it may bear and be sus tained on both sides of the paintedportion.

It is manifest that the staff painted and applied as above cannot applythe paint to depressed points in the stone, and that, being sustained atall times on both sides of the paint, the latter will not be appliedwith any greater distinct-ness on the soft portions than on the others.

In the drawings, Figure 1 represents a plan view of a stone having myred-staff applied thereto. Fig. 2 is a perspective view of the staff.

The staff 13, being painted in the manner shown, is laid across thestone in any position desired and carried over the same in differentdirections at will until every point in the grinding-surface has beenpassed over by the paint. The depressed points will remain unpainted.Whenever the entire surface can be painted the stone will be foundperfectly true and straight. After the grinding-face is trued the bosomis sunk to a lower level, as usual.

I am aware that a staff has been painted at the center, laiddiametrically across the stone, and then rotated while retaining thediametric position, in order to paint the bosom in a circular form.This, however, has no bearing on my invention, inasmuch as it was notapplied to test the grinding-surface, but required the latter to betrued first, for which purpose a special and entirely dissimilar devicewas provided. I

I believe myself to be the first to test the grinding-surface by meansof a staff having paint on a small central portion only; and myinvention consists, broadly, in so doing, whether the paint is appliedin the exact middle of the staff or not, and without reference to theexact length of the painted portion, provided it is quite small ascompared with the length of the staff.

Having thus described my invention, what I claim is- Theherein-described method of truing the grinding faces of millstones,consisting in applying a straight staff having a small painted portionat the center, and moving the staff over the stone in such manner as topass the paint over every portion of the grinding-surface, substantiallyas described and shown.

WILLIAM LEHMANN.

Witnesses:

JACOB RICHTER, LoUIs KLINOKERFUES.

